The concept of broadband (or, wideband) communication is well-known. Simplistically, broadband communication techniques attempt to reduce the impact of fading by communicating information over a wideband channel employing convolutional coding and interleaving to redundantly distribute the information across the wideband channel. The phenomenon of frequency-selective fading of radio signals is a well-known obstacle to reliable wireless communication. Since fading is frequency sensitive, spreading a channel across a number of frequencies reduces the likelihood that the entire channel will suffer from the fading, and increases the likelihood of that enough of a signal is received at the receiver to reconstitute a substantial representation of the transmitted signal.
One example of a broadband communication technique employs Orthogonal Frequency Division Multiplexing (OFDM) digital modulation. OFDM describes a general class of digital modulation techniques where a set of equally spaced, phase synchronous sub-carriers are independently modulated with relatively low-rate user data in order to create a high-rate modulated waveform which can be demodulated by means of a fast-Fourier transform and sub-carrier phase detection.
OFDM is employed in several broadband applications including, for example, Digital Subscriber Line (xDSL) applications as well as the emerging wireless Ethernet standard IEEE 802.11a (IEEE Standard No: 802.11A-1999, ISBN:0-7381-1810-9) , incorporated herein for all purposes. Digital signals transmitted according to the 802.11a standard undergo convolutional coding, interleaving and distribution among the sub-channels. The redundancy and decorrelation of errors provided by the coding, interleaving and distribution effectively provides a signal that is robust against frequency-selective fading as it propagates through the channel. If, as can often be the case, certain of the sub-carriers are impaired by frequency selective fading, it is hoped that enough of the sub-carriers remain unimpaired such that most of the original signal is recovered at the receiver.
In order for this process to be successful however, it is necessary that the fading is sufficiently frequency selective, and that not all (or a large fraction) of the sub-carriers become simultaneously faded. If such a situation were to arise, even the redundant bits may be lost, causing irreparable data loss. In this regard, wideband communication systems such as the OFDM system introduced above, operate best when fading of each sub-carrier is decorrelated from the fading of other sub-carriers. The difficulty in arranging for such decorrelation between the sub-carriers of the wideband communication channel contributes to the lack of widespread adoption of this standard.
Thus, a means for improving the ability of a wideband communication signal to withstand less than ideal channel conditions is required, unencumbered by the limitations commonly associated with conventional communication techniques. More particularly, a system and related methods for introducing sub-carrier diversity in a wideband communication system is required.